Human serum lipoproteins are complexes in which the protein moiety is able to interact with large molar ratios of phospholipid, cholesterol, cholesteryl ester, and triglycerides - maintaining these amphiphilic substances in a water soluble state. It is the purpose of this research to elucidate the nature of these interactions together with the structure of the lipoprotein complexes as a function of amphiphilic ligand binding. Specifically, we will investigate ternary complexes of phospholipid cholesterol-AI (or AII) and phospholipid-cholesterylester-apoB. The mode of ligand interaction, maximum binding, synergism among ligands, and structural properties of the complexes will be determined. The interaction of the homogeneous, well-characterized complexes with in vivo receptors for different classes of lipoproteins will be investigated.